This invention relates to systems and methods for control of vehicle engines and, in particular, to a system and method for determining values for engine control variables.
Conventional vehicle engines are electronically controlled through the use of a programmable electronic control unit (xe2x80x9cECUxe2x80x9d). The ECU is used to monitor engine performance and to control the operation of a wide variety of engine components such as fuel injectors, camshaft actuators, spark plugs and the throttle valve. In controlling the various engine components, the ECU determines values for a wide variety of control variables.
In recent years advances such as variable cam timing, variable valve lift, and charge motion control have introduced additional degrees of freedom and increased complexity to engine control. One method of dealing with this increased complexity has been to schedule only limited sets of values for control variables-typically those values encountered during steady state operation of the engine. This method suffers from a significant drawback, however. During transient operation of the engine, the speed of the engine, the load on the engine, and the position of engine components such as the camshaft(s) reach new steady state values at different rates. As a result, the actual values for various engine control variables may be quite different from the scheduled values during transient operation. This can lead to a variety of problems. For example, spark timing may not be optimized leading to engine knock, increased fuel consumption and reduced driveability.
There is thus a need for a system and method for determining the value for a control variable for an engine that will minimize and/or eliminate one or more of the above-identified deficiencies.
The present invention provides a system and a method for determining the value for a control variable for an engine. The engine may comprise a conventional fuel-injected internal combustion engine and may define a plurality of cylinders in which intake and exhaust valves are opened and closed to control the delivery and exhaust of air and fuel.
A method in accordance with the present invention includes the step of obtaining a plurality of pairs of programmed timing values for intake valve opening and exhaust valve closing in a cylinder of the engine responsive to a speed of the engine and a load on the engine. Each pair of the plurality of pairs of programmed timing values is based on a different one of a plurality of sets of predetermined operating conditions for the engine. For example, one set of operating conditions may include a condition in which the camshaft actuator is locked. Another set of operating conditions may include a condition corresponding to a predetermined altitude and a condition of optimal output torque for the engine.
The inventive method may also include the step of obtaining a plurality of conditional values for the control variable, each conditional value of the plurality of conditional values responsive to the speed, the load, and a different one of the plurality of pairs of programmed timing values. Finally, the inventive method may include the step of determining the value for the control variable responsive to the plurality of conditional values for the control variable. In particular, the determining step may include an interpolation between the previously determined conditional values for the control variable using an interpolation method such as the xe2x80x9cinverse distancexe2x80x9d method.
A system in accordance with the present invention includes an electronic control unit that is configured to perform several functions. In particular, the unit is configured to obtain a plurality of pairs of programmed timing values for intake valve opening and exhaust valve closing in a cylinder of the engine responsive to a speed of the engine and a load on the engine, each pair of the plurality of pairs of programmed timing values based on a different one of a plurality of sets of predetermined operating conditions for the engine. The unit is further configured to obtain a plurality of conditional values for the control variable, each conditional value of the plurality of conditional values responsive to the speed, the load, and a different one of the plurality of pairs of programmed timing values. Finally, the unit is configured to determine the value for the control variable responsive to the plurality of conditional values for the control variable.
The present invention represents an improvement as compared to conventional systems and methods for determining values for control variables for an engine. In particular, the inventive system and method improve engine performance during transient conditions by enabling a more accurate determination of optimal values for control variables without requiring increased scheduling of the control variables.
These and other advantages of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.